(1) Field of the Invention
The invention relates to novel polyesters of the linear and rodlike type consisting essentially of specified recurring units that will not only ascertain melting points of below 350.degree. C. but also provide controlled rigidity and packing density of the macromolecules. Further, the invention relates to polymer blends containing the novel polyesters; to copolyesters that contain the specified recurring units; th articles of manufacture consisting of the novel polyesters, polymer blends, or copolyesters; and to methods of producing novel polyesters.
(2) Description of the Prior Art
It is known in the art that polymers with greatly improved mechanical properties can be obtained if the coiled chains of conventional thermoplastic polymers, such as polyethylene, are stretched such that the molecules attain a more or less rodlike structure. Such rodlike macromolecules, however, can be easily obtained in polymers whose recurring units mainly consist of cyclic units, e.g. phenylenic or naphthenic and sometimes cycloaliphatic moieties linked typically by covalent bonds, carboxyl or amide groups.
Yet, when the molecular chains of conventional polyamides were made more rigid by incorporation of phenylenic moieties, the resulting aromatic polyamides or aramides (e.g. KEVLAR, reg. trademark by E. I. DuPont), while showing subtantially improved mechanical properties, were not processable in the molten state and are only soluble in unusual or corrosive solvents, such als sulphuric acid.
In an analogous manner the backbone chains of polyesters have been modified so as to improve mechanical and other properties by increasing the rigidity of the polymer chains. However, when significant improvements of the mechanical properties were achieved, the resulting linear polyesters did not melt below, or not substantially below, their decomposition temperature and the solubility in organic solvents was poor at best.
Numerous attempts towards improved polyesters have been disclosed in the literature, e.g. in the following patent specifications: GB Pat. No. 989,552 and 993,272; U.S. Pat. Nos. 4,067,852, 4,102,864, 4,118,372, 4,161,470, 4,184,999, 4,219,461, 4,327,206: EP Pat. Nos. 28,030, 72,540, 139,924 and 212,944. The teachings of these patents can be summarized in that polyester-type condensates having rigid and/or rodlike chains with excellent mechanical properties can be obtained but that high melt processing temperatures will be required if the products can be processed by such methods at all. Further, previous attempts to modify the rodlike molecules are based upon the introduction of either flexible aliphatic groups as links between the aromatic moieties, or by introducing "kinks", i.e. elements of controlled angularity in the links between adjacent cyclic moieties, into the rodlike polymer chains. In both cases the macromolecules will not be rodlike; further, rigidity of the polymer molecules may be lost or substantially decreased by such modifications and, while melting temperatures in the range of between 250.degree. and 350.degree. C. were reported for such polymers, the mechanical properties of the melt processed polymers have been adversely affected to the point that little if any improvements of practical importance were achieved.
Specifically, if kinks were introduced into the molecular chain of prior art rodlike polyesters, this was done by using the ortho- or meta-isomers instead of the para-constituents, or by interconnecting the cyclic moieties via linkages that contain an odd number of atoms in the backbone or main chain, e.g. one or three and not two or four atoms, between adjacent cyclic moieties.
Further, some prior art patents disclose or claim copolyesters in which the recurring units or parts thereof are undefined and where the polymer chain is allowed to include non-fusible segments so that the resulting molecules cannot be properly oriented upon processing. This, in turn, will cause mechanical defects in the oriented structure leading to an appreciable deterioration of the mechanical properties of the resulting material.
Finally, the art includes many generic structures without the specific support required to derive a generally operable teaching of commensurable scope.
Accordingly, it is the object of the present invention to provide well-defined linear rodlike polyesters, i.e. having rodlike chains, in which the chain rigidity and packing density can be controlled so as to provide melting temperatures in the range of from 100.degree. to 350.degree. C. without an offsetting loss of mechanical properties.